Some geological features worthy of note were observed in the course of oil explorations near Petaluma, in the foothill belt between the tide flats and alluvial plain of lower Petaluma Creek and the rugged area of Sonoma Mountain (Fig. 1, and the Petaluma and Santa Rosa sheets of the United States Geological Survey). Of particular interest are certain stratigraphic and fault features disclosed in mapping and in the study of cores from five wells drilled in the southeastern half of this belt, some 5 miles east of the town of Petaluma and 33 miles north of San Francisco.
The area closely studied is small, but it discloses relationships characteristic of a much larger area in the central Coast Range, concerning which comparatively little has been published. Recognition of certain features here shown may help to lead to a clearer understanding of the relationships with the better known region of . . .